Manufacturing method of composite electrode material

ABSTRACT

Provided is a manufacturing method of a composite electrode material which includes the following steps. An electro-deposition device is provided. The electro-deposition device includes a mixed solution and a working electrode and an auxiliary electrode placed in the mixed solution. The mixed solution includes a conductive material precursor and an active material precursor. An alternating voltage is applied to the electro-deposition device, so as to perform a plurality of electrochemical reactions on a surface of the auxiliary electrode and therefore to form a composite electrode material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 105113269, filed on Apr. 28, 2016. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to a manufacturing method of an electrodematerial, and more particularly to a manufacturing method of a compositeelectrode material.

Description of Related Art

An energy storage technique usually indicates a storage of electricenergy, mainly including an energy storage with physical properties(e.g., a capacitor), an energy storage with electrochemical properties(e.g., a battery) or a combination thereof (e.g., a supercapacitor).

Generally speaking, an electrode material of the energy storage deviceis usually manufactured with a slurry coating, a chemical vapourdeposition, a DC electroplating or a DC electrophoresis. However, theabove method requires a mixing or a stage-by-stage approach to preparethe electrode material. Such method is time-consuming and the electrodematerial cannot be sufficiently mixed. Therefore, poor contact existsbetween the components of the electrode material, such that theelectrochemical properties of the energy storage device decrease (e.g.,a low specific capacitance) and a rapid decline in specific capacitanceat a high-speed charging/discharging are observed.

SUMMARY OF THE INVENTION

The present invention provides a manufacturing method of a compositeelectrode material. The composite electrode material is manufacturedwith a high specific capacitance, and such high specific capacitance canbe maintained at a high-speed charging/discharging.

The present invention also provides a manufacturing method of acomposite electrode material which includes the following steps. Anelectro-deposition device is provided. The electro-deposition deviceincludes a mixed solution and a working electrode and an auxiliaryelectrode placed in the mixed solution. The mixed solution includes aconductive material precursor and an active material precursor. Analternating voltage is applied to the electro-deposition device, so asto perform a plurality of electrochemical reactions on a surface of theauxiliary electrode and therefore to form a composite electrodematerial.

In view of the above, in the present embodiment, a composite electrodematerial is formed on the surface of an auxiliary electrode by applyingan alternating voltage to an electro-deposition device. The conductivematerial layers and the active material layers of the compositeelectrode material are stacked alternately along the directionnon-parallel to the surface of the electrode, and are arrangeddisorderly along the direction parallel to the surface of the electrode.By such manner, the bonding properties between the conductive materiallayers and the active material layers can be improved, and theconductive material layers and the active material layers can besufficiently mixed. Accordingly, the energy storage device including thecomposite electrode material of the present embodiment can maintain ahigh specific capacitance at a high current densitycharging/discharging. That is, the energy storage device including thecomposite electrode material of the present embodiment can significantlyreduce the charging time so as to meet the users' requirements.

Besides, in the manufacturing method of the present embodiment, astacked composite electrode material can be formed merely with aone-step method. Therefore, the performance of simplifying the processand reducing the cost can be easily achieved with the manufacturingmethod of the present embodiment.

In order to make the aforementioned and other objects, features andadvantages of the present invention comprehensible, a preferredembodiment accompanied with figures is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic cross-sectional view of a composite electrodematerial according to an embodiment of the present invention.

FIG. 2 is a schematic view of an electro-deposition device according toan embodiment of the present invention.

FIG. 3 is a cyclic voltammetry curve of the composite electrode materialof Example 1.

FIG. 4 is a resulting curve of a charging/discharging test of thecomposite electrode material of Example 1.

FIG. 5 is resulting curve of an AC impedance of the composite electrodematerial of Example 1.

FIG. 6A is a graph showing the relationship between the current densityand the specific capacitance of a conventional electrode material.

FIG. 6B is a graph showing the relationship between the current densityand the specific capacitance of the composite electrode material ofExample 1.

DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. The invention may, however, be embodied in otherforms and should not be construed as being limited to the embodimentsset forth herein. In the following embodiments, the directionalterminology, such as “top,” “bottom,” or the like, is used withreference to the orientation of the Figure(s) being described. As such,the directional terminology is used for purposes of illustration and isin no way limiting. Besides, the dimensions or thicknesses of layers andregions are exaggerated for clarity. Wherever possible, the same or likereference numbers are used in the drawings and the description to referto the same or like parts.

FIG. 1 is a schematic cross-sectional view of a composite electrodematerial according to an embodiment of the present invention.

Referring to FIG. 1, the present embodiment provides a compositeelectrode material 100 disposed on a surface S1 of an electrode 110. Inan embodiment, the electrode 110 includes a conductive material, such asplatinum (Pt) or another metal material, but the present invention isnot limited thereto. Besides, the type of the electrode 110 is notlimited by the present invention. For example, the electrode 110 can bean electrode plate or a porous/foam electrode or another type of theelectrode.

Specifically, the composite electrode material 100 includes a pluralityof stacked structures 100 a, 100 b, 100 c and 100 d. For example, thestacked structure 100 a has N+1 conductive material layers 102 a and Nactive material layers 104 a, wherein N is an integer equal to orgreater than 1. As shown in FIG. 1, one active material layer 104 a islocated between two adjacent conductive material layers 102 a, and thelowest first conductive material layer 102 a is in contact with thesurface S1 of the electrode 110.

The stacked structure 100 b has i+1 active material layers 104 b and iconductive material layers 102 b, wherein i is an integer equal to orgreater than 1. As shown in FIG. 1, one conductive material layer 102 bis located between two adjacent active material layers 104 b, and thelowest active material layer 104 b is in contact with the surface S1 ofthe electrode 110.

The stacked structure 100 c has N conductive material layers 102 c and Nactive material layers 104 c, wherein N is an integer equal to orgreater than 1. As shown in FIG. 1, the conductive material layers 102 cand the active material layers 104 c are stacked alternately along thedirection D1 perpendicular to the surface S of the electrode 110, andthe lowest conductive material layer 102 c is in contact with thesurface S1 of the electrode 110.

The stacked structure 100 d has i conductive material layers 102 d and iactive material layers 104 d, wherein i is an integer equal to orgreater than 1. As shown in FIG. 1, the conductive material layers 102 dand the active material layers 104 d are stacked alternately along thedirection D1 perpendicular to the surface S1 of the electrode 110, andthe lowest active material layer 104 d is in contact with the surface S1of the electrode 110.

It is noted that, the embodiment of FIG. 1 in which only four stackedstructures are shown and the conductive material layers and the activematerial layers are stacked alternately along the directionperpendicular to the surface of the electrode is provided forillustration purposes, and is not construed as limiting the presentinvention. In another embodiment, the number of the stacked structurescan be one, two, three or more than four. Stacked structures arecontemplated as falling within the scope of the invention as long as theconductive material layers and the active material layers of suchstacked structures are stacked alternately along the direction D1 or D3non-parallel to the surface S1 of the electrode 110, and are arrangeddisorderly along the direction D2 parallel to the surface S1 of theelectrode 110. Herein, the direction D1/D3 non-parallel to the surfaceS1 of the electrode 110 can be the direction D1 perpendicular to thesurface of the electrode or the direction D3 which forms an includedangle θ (θ is not zero) with the direction D2 parallel to the surface S1of the electrode 110. In other words, a direction is contemplated asfalling within the scope of the invention as long as such direction isnot the direction D2 that is parallel to the surface S1 of the electrode110. The term “arranged disorderly” indicates that multiple stackedstructures can be arranged in a staggered or random manner. In otherwords, the conductive material layers and the active material layers ofthe present embodiment can be sufficiently mixed, so as to increase thecontact areas between the conductive material layers and the activematerial layers. Therefore, during the charging/discharging operation,the electrons generated from the active material layers can be quicklytransmitted by the conductive material layers, so as to improve thecharging/discharging efficiency. On the other hand, as compared to theconventional single active material layer, multiple active materiallayers of the present embodiment can provide a greater effectivereaction area. That is, in the present embodiment, the effectivereaction area between the active material layers and the electrolytesolution of the energy storage device is increased, so the specificcapacitance of the energy storage device is accordingly improved.

Besides, the stacked structures 100 a, 100 b, 100 c and 100 d in FIG. 1are not in contact with each other and are separated by a distance.However, the present invention is not limited thereto. In anotherembodiment, the sidewalls of the stacked structures 100 a, 100 b, 100 cand 100 d are in contact with each other, or the sidewalls of only partsof the stacked structures 100 a, 100 b, 100 c and 100 d are in contactwith each other.

In an embodiment, the material of each of the conductive material layers102 a-102 d includes a conductive material such as graphene, a graphenederivative, nanotubes, a monomer for a conductive polymer, or acombination thereof. The graphene derivative can be a doped graphene, anundoped graphene, a doped graphene oxide, an undoped graphene oxide, ora combination thereof. The monomer for the conductive polymer can beaniline. Each of the conductive material layers 102 a-102 d has athickness of about 0.3 nm to 10 μm.

In an embodiment, the material of each of the active material layers 104a-104 d can be a positive active material or a negative active material.That is, the composite electrode material 100 of the present embodimentcan be applied to a positive electrode or a negative electrode dependingon the materials or species of the active material layers. For example,the material of each of the active material layers 104 a-104 d can be ametal oxide, a metal hydroxide, a metal oxysulfide, a metal sulfide, ametal fluoride, a metal or a combination thereof. Each of the activematerial layers 104 a-104 d has a thickness of about 0.3 nm to 10 μm.

The manufacturing method of the composite electrode material 100 of theabove embodiment is described in the following. The manufacturing methodof the present invention is illustrated below with reference to theelectro-deposition device and the cross-sectional view of the compositeelectrode material 100.

FIG. 2 is a schematic view of an electro-deposition device according toan embodiment of the present invention.

Referring to FIG. 2, the present embodiment provides a method ofmanufacturing a composite electrode material by an electro-depositiondevice which includes the following steps. First, an electro-depositiondevice 200 is provided. Specifically, the electro-deposition device 200includes a reaction device 210, a working electrode 204, an auxiliaryelectrode 206 and a power supply 208.

Thereafter, a mixed solution 202 is placed in the reaction device 210.In an embodiment, the reaction device 210 can be a beaker, a culturedish or a suitable vessel which is adapted for containing the mixedsolution 202 without chemically reacting with the mixed solution 202.

Specifically, the mixed solution 202 includes a conductive materialprecursor and an active material precursor. In an embodiment, theconductive material precursor includes a conductive material such asgraphene, a graphene derivative, nanotubes, a monomer for a conductivepolymer, or a combination thereof. The graphene derivative can be adoped graphene, an undoped graphene, a doped graphene oxide, an undopedgraphene oxide or a combination thereof. The monomer for the conductivepolymer can be aniline. The active material precursor can be a metalsalt, and the metal salt includes a metal nitride, a metal acetate, ametal sulfate, or a combination thereof.

Afterwards, the working electrode 204 and the auxiliary electrode 206are dipped in the mixed solution 202, and one terminal of the powersupply 208 is electrically connected to the working electrode 204 andanother terminal of the power supply 208 is electrically connected tothe auxiliary electrode 206. In an embodiment, the working electrode 204and the auxiliary electrode 206 can be platinum electrodes which are noteasily eroded or consumed by chemically reacting with the mixed solution202. In another embodiment, the electro-deposition device 200 canfurther include a reference electrode.

An alternating voltage is then applied to the auxiliary electrode 206 bythe power supply 208, such that a plurality of electrochemical reactionsare carried out on the surface of the auxiliary electrode 206, and thecomposite electrode material 100 of FIG. 1 is thus formed. In anembodiment, the composite electrode material 100 has a specificcapacitance of about 2,000 F/g to 3,000 F/g. At a high current density(e.g., 10 A/g) charging/discharging, the composite electrode material100 still has a specific capacitance of about 2,000 F/g to 3,000 F/g. Inan embodiment, each of the electrochemical reactions can be anoxidation-reduction reaction, an electrophoretic deposition or acombination thereof.

Specifically, the electro-deposition device 200 of the presentembodiment is constantly switched between a high voltage mode and a lowvoltage mode. The conductive material precursor in the mixed solution202 is transformed into conductive material layers in the high voltagemode, while the active material precursor in the mixed solution 202 istransformed into active material layers in the low voltage mode. Sincethe manufacturing method is a deposition technique at an atomic scale,the conductive material layers and the active material layers can beuniformly stacked by multiple switching between high and low voltages.The conventional technique such as a precipitation method or a slurrymethod has the issue that materials per se are aggregated withoutcontacting the electrode, so the performance of the energy storagedevice is degraded. The present embodiment accordingly provides a methodto solve the above conventional issue.

In an embodiment, the alternating voltage can be a pulse voltage, an ACvoltage (e.g., a sine-wave AC voltage) or a cycle voltage. However, thepresent invention is not limited thereto. In another embodiment, anoperation is contemplated as falling within the scope of the presentinvention as long as such operation includes continuously switchingbetween high and low voltages applied to the auxiliary electrode 206. Inanother embodiment, the high voltage can be a positive voltage, and thelow voltage can be a negative voltage.

In addition, in the present embodiment, the thickness of each of theconductive material layers and the active material layers can beadjusted by changing the pulse period. That is, when the pulse period isdecreased, the oxidation-reduction reaction is carried out for a shortertime, and each of the conductive material layers and the active materiallayers is accordingly formed thinner. Besides, in the presentembodiment, the number of the stacked layers can be controlled bychanging the total electro-deposition time. That is, when the totalelectro-deposition time is increased, the total number of the conductivematerial layers and the active material layers is accordingly increased.

Besides, an alternating voltage can be applied to a roll-to-rollelectroplating device, in addition to the electro-deposition device 200,so as to form a composite electrode material. The roll-to-rollelectroplating device can be used for mass production with a reducedprocess cost, and thus, the competitive advantage can be easilyachieved.

In order to prove the feasibility of the present invention, severalexperiments are provided below to further illustrate the compositeelectrode material of the present invention. Experiments are providedbelow to more specifically describe the invention. Although thefollowing experiments are described, the materials used and the amountand ratio of each thereof, as well as handling details and handlingprocedures, etc., can be suitably modified without exceeding the scopeof the invention. Accordingly, restrictive interpretation should not bemade to the invention based on the experiments described below.

Example 1

First, a graphene oxide was prepared through a Hummer's method.Specifically, 720 mL of H₂SO₄ and 80 mL of H₃PO₄ were uniformly mixed.Thereafter, 3 g of graphene and 12 g of KMnO₄ were added to the mixture,the reaction temperature was increased to 60 C and the mixture wasreacted for 18 hours. Afterwards, 600 mL of ice cubes (prepared bydeionized water) and 5-10 mL of H₂O₂ were added to the mixture to stopthe reaction. The mixture was then washed several times with deionizedwater, hydrochloric acid and ethanol, filtered by a glass fiber filter,and finally centrifuged. Next, ether was added to the mixture, filteredby a polytetrafluoroethylene (PTFE) filter with a pore size of 0.2 μm,and finally vacuum baked at 40° C. for 12 hours, and a solid grapheneoxide was thus obtained.

Afterwards, 2 mM of Ni(NO₃)₂ and 4 mM of Co(NO₃)₂ were prepared in a0.01 M phosphate buffered saline (PBS, pH=7.4) solution, and a grapheneoxide PBS solution in which the graphene oxide had a weight equal to thetotal weight of Ni(NO₃)₂ and Co(NO₃)₂ was added thereto, and the mixturewas fully stirred. A potentiostat (CH Instruments, CHI 608) with a foamnickel as a working electrode, a standard calomel electrode as areference electrode and a platinum electrode as an auxiliary electrodewas used, and 200 pulse signals were applied, so as to prepare agraphene/nickel-cobalt hydroxide composite electrode material(abbreviated “composite electrode material of Example 1” hereinafter).In Example 1, the graphene layer has a thickness of about 10 nm to 100nm, and the nickel-cobalt hydroxide layer has a thickness of about 10 nmto 100 nm.

Afterwards, the composite electrode material of Example 1 was placed ina vacuum oven to remove water, the electrochemical properties thereofwere measured with a potentiostat (CH Instruments, CHI 608), and theresults were shown in FIG. 3, FIG. 4 and FIG. 5.

FIG. 3 is a cyclic voltammetry curve of the composite electrode materialof Example 1. FIG. 4 is a resulting curve of a charging/discharging testof the composite electrode material of Example 1. FIG. 5 is resultingcurve of an AC impedance of the composite electrode material of Example1.

As shown in FIG. 3, the composite electrode material of Example 1 has areversible oxidation and reduction property. The composite electrodematerial of Example 1 has an oxidation peak potential of about 0.25 Vand a reduction peak potential of about 0.075 V at a scan rate of 5mV/s. That is, the composite electrode material of Example 1 is formedwith a charging/discharging property.

Afterwards, a charging/discharging test is performed to the compositeelectrode material of Example 1 in a constant current mode, and theresults are shown in FIG. 4. The composite electrode material of Example1 has a charging time of about 2,300 seconds at a current density of 1A/g, and has a charging time of about 235 seconds at a current densityof 10 A/g. That is, the charging time of the composite electrodematerial of Example 1 can be quickly shortened at a high currentdensity. When such composite electrode material is applied to an energystorage device, the energy storage device can be charged more quicklythan a conventional energy storage device, either in a constant currentmode or under the case of charging the same capacitance. Specifically,since no conductive layer or merely single conductive layer is includedin the conventional energy storage device, an issue which electronscannot be transmitted rapidly at a high current density is generated.Based on the above, the issue of the conventional energy storage devicecan be resolved by the present invention.

As shown in FIG. 5, when the composite electrode material of Example 1is applied to an energy storage device, the composite electrode materialof Example 1 has a smaller internal resistance of about zero Ohms. Thatis, the composite electrode material of Example 1 is formed withoutexcessive impedance leading to a reduction in charging/dischargingperformance.

In addition, the specific capacitance of the composite electrodematerial of Example 1 can be calculated from the data from FIGS. 3-5 andthe following equation.

C=I×Δt/ΔV×m  (1)

wherein I is the current density, Δt is the charging/discharging time, mis the mass of the sample, and ΔV is the working voltage.

FIG. 6B is a graph showing the relationship between the current densityand the specific capacitance of the composite electrode material ofExample 1 calculated from the above equation. FIG. 6A is a graph showingthe relationship between the current density and the specificcapacitance of a conventional electrode material. The so-calledconventional electrode material indicates a single nickel-cobalthydroxide layer coated on the electrode.

Referring to FIG. 6A and FIG. 6B, the specific capacitances (about2,800-3,000 F/g) of the composite electrode material of Example 1 atdifferent current densities (i.e., 1, 3, 5, 10 A/g) are all higher thanthe specific capacitance (about 1,000-2,300 F/g) of the conventionalelectrode material. On the other hand, the composite electrode materialof Example 1 still has a high specific capacitance of about 2800-3,000F/g at a high current density of 10 A/g. On the contrary, the specificcapacitance of the conventional electrode material is reduced to 1,000F/g at a high current density of 10 A/g. That is, the compositeelectrode material of the present invention can effectively solve theissue of rapid decline in specific capacitance at a high currentdensity.

Therefore, the present invention can solve the issue of long chargingtime of the conventional energy storage device. The energy storagedevice including the composite electrode material of the invention canbe provided with a shorter charging time and thus drawn attention fromconsumers in terms of a commercial product. For example, the energystorage device is beneficial for a green energy field. When such energystorage device is applied to an electric vehicle, the fossil energyconsumption and therefore the carbon emissions can be reduced, and thegreenhouse effect can be alleviated.

In summary, in the present embodiment, a composite electrode material isformed on the surface of an auxiliary electrode by applying analternating voltage to an electro-deposition device. The conductivematerial layers and the active material layers of the compositeelectrode material are stacked alternately along the directionnon-parallel to the surface of the electrode, and are arrangeddisorderly along the direction parallel to the surface of the electrode.By such manner, the bonding properties between the conductive materiallayers and the active material layers can be improved, and theconductive material layers and the active material layers can besufficiently mixed. Accordingly, the energy storage device including thecomposite electrode material of the present embodiment can maintain ahigh specific capacitance at a high current densitycharging/discharging. That is, the energy storage device including thecomposite electrode material of the present embodiment can significantlyreduce the charging time so as to meet the users' requirements.

Besides, in the manufacturing method of the present embodiment, astacked composite electrode material can be formed merely with aone-step method. Therefore, the performance of simplifying the processand reducing the cost can be easily achieved with the manufacturingmethod of the present embodiment.

The present invention has been disclosed above in the preferredembodiments, but is not limited to those. It is known to persons skilledin the art that some modifications and innovations may be made withoutdeparting from the spirit and scope of the present invention. Therefore,the scope of the present invention should be defined by the followingclaims.

What is claimed is:
 1. A manufacturing method of a composite electrodematerial, comprising: providing an electro-deposition device, whereinthe electro-deposition device comprises: a mixed solution, having aconductive material precursor and an active material precursor; and aworking electrode and an auxiliary electrode, placed in the mixedsolution; and applying an alternating voltage to the electro-depositiondevice, so as to perform a plurality of electrochemical reactions on asurface of the auxiliary electrode and therefore to form a compositeelectrode material.
 2. The manufacturing method of claim 1, wherein thealternating voltage comprises a pulse voltage, an AC voltage or a cyclevoltage.
 3. The manufacturing method of claim 1, wherein the conductivematerial precursor comprises a graphene, a graphene derivative, carbonnanotubes, a monomer for a conductive polymer or a combination thereof.4. The manufacturing method of claim 1, wherein the active materialprecursor comprises a metal salt, and the metal salt comprises a metalnitride, a metal acetate, a metal sulfate or a combination thereof. 5.The manufacturing method of claim 1, wherein each of the electrochemicalreactions comprises an oxidation-reduction reaction, an electrophoreticdeposition or a combination thereof.
 6. The manufacturing method ofclaim 1, wherein the electro-deposition device comprises a roll-to-rollelectroplating device.
 7. The manufacturing method of claim 1, whereinthe composite electrode material comprises: a plurality of conductivematerial layers; and a plurality of active material layers, wherein theconductive material layers and the active material layers are stackedalternately along a direction non-parallel to the surface of theauxiliary electrode, and are arranged disorderly along a directionparallel to the surface of the auxiliary electrode.
 8. The manufacturingmethod of claim 1, wherein the composite electrode material comprises: aplurality of first stacked structures, disposed on the surface of theauxiliary electrode, wherein each of the first stacked structures has atleast one first conductive material layer and at least one first activematerial layer, wherein the first conductive material layer is incontact with the surface of the auxiliary electrode; and a plurality ofsecond stacked structures, disposed on the surface of the auxiliaryelectrode, wherein each of the second stacked structures has at leastone second conductive material layer and at least one second activematerial layer, wherein the second active material layer is in contactwith the surface of the auxiliary electrode, wherein the first stackedstructures and the second stacked structures are arranged disorderlyalong a direction parallel to the surface of the auxiliary electrode.